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Fiberglass Repair

Getting started/Tools

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Basic tools list for fiberglass repair.
Angle grinder 4". (100mm)
Sanding pad.
Sanding disc/s.
Mixing container/s.
Spatula. (optional)
Sanding block. (optional)
Laminate roller. (optional)

Goggles/safety glasses.
Gloves. (optional)

An indepth look at the basic tools we need to repair fibreglass.

If we have not done fibreglass repair work before we usually ask ourselves, apart from how to repair fiberglass and that is "what tools do I need?"

I will show you a list of tools and accessories that you may or will
need depending on the size and type of fiberglass repair that you have and if your a handyman or a handywoman you may well have already most of these tools!

But I will take it that you have none, that way you will know what to
beg, borrow (off your friends) or better still, is to buy what you don't
have yourself.

So, we have our fiberglass item that needs repair and have found a suitable location to do the job.

The tools that we need to repair fiberglass are usually fairly basic, so
one of the most common used tools for fiberglass repair is a electric
angle grinder with a sanding pad and disc put in place where the
grinding wheel is located on the shaft.

Grinders :

The most common size grinder that we will use when doing fiberglass repair will be a 100mm (4") or a 125mm (5") grinder or upwards for larger work and/or heavy laminates.

When choosing a grinder it is most important to choose one that fits
your hand grip as some grinders have a large body (higher wattage motor) and can be awkward to handle even with a handle attached.

Large bodied 100mm grinders will tend to kick or twist in your hand
when they start up, so if you have a small hand they can give you a
feeling of un-easiness, especially if your working in tight areas.
100 mm and 125mm grinders
Switches on a grinder can be equally important
as some are located on the sides, the top as a slide switch, at the bottom as a trigger switch or at the rear of the machine as a toggle switch.

So, it will be personal choice here to choose but
if you are planning on doing a lot of fiberglass repair work or sanding woods etc. then a rear mount toggle switch or a trigger switch will be your best choice as from personal experience.

We have had many grinders in the past and still use one with a slide switch as they are handy to switch on and off but after a while dust
and fibers collect and works itself inside the machine causing the
grinder to fail or turn off and on Grinder maintenance whilst being in use which can be very annoying and somewhat dangerous, especially when you turn off the grinder or go to unplug it and it comes on unexpectedly, these type of grinders need pulling apart and cleaning (air dusting/blowing out with compressed air) more often than the others.

So, are expensive brands better than cheaper brands? Well I have
had both and many over the years of going fiberglass repair and have found that both fail to the same cause and usually around the same
times given similar work loads.

The cause of failure is either the commutator and/or bearings or
both, as grinding dust is very abrasive to the windings and bearings inside the grinders.

I usually use mid price grinders around the $35 - $50 mark, I seen
a grinder around $20 bucks it even came with a 2 year warranty but
they were all sold out, next time I see them I will check it out and put
it to the test and let you know how it goes, if it does go that is!

By the way, while on the subject of grinders, if you have ever
replaced the brushes in a grinder you may have known the frustration
and /or time it can take pulling apart and changing brushes in a faulty
machine (for most people it is a trip to the electrical repair shop) it is
far better to look for one that has easy external access to the brushes (see photo example) as these can wear out (even if not being used for fiberglass repair work).

Sanding discs :
sanding discs

For doing fiberglass repairs we need to make sure we prepare our surface well to obtain a good bond, so our new materials get a good grip to the existing laminate.

These discs have on the sanding surface (specially the P16/24 grit) very course sharp grits which are usually silicon carbide so wearing masks, safety glasses or goggles are a must!

There are many brands available, but if you intend to do a lot of fiberglass repairs then Metalite or Norton discs will last longer.

Mixing containers :

For small fiberglass jobs like a broken car rear wing, spoiler, flares,
side skirts, canoe, cracks in a fiberglass boat, car or a child's fiberglass rocking horse as an example, any clean tin or even an old microwave container to take enough resin to do the job will do, make sure you wash and dry the container thoroughly before use.

Try not to use tins that have had such things as seafood, fish or any
sort of tins that have contained oil products, even if washed, oil residue could remain in the tin coating as this might contaminate the
resin and product failure could occur.

Assorted mixing containers. For larger jobs plastic 1ltr, 2ltr or 4ltr ice cream containers are great for big jobs like fiberglass stern replacements, hull bearer replacement and or floor replacements in GRP/FRP boats (fiberglass boats) or any job requiring larger quantities of a resin mix.


Not all plastic containers are suitable to mix polyester resin in as polyester based resins, even if not catalyzed can quite easily start to deform/melt or
even liquefy the bottom of the container causing leakage and or collapse of
the container if left too long.

Plastic containers not suitable for resin mixes are butter or margarine
containers, yogurt, fruit snack and alike. Glass jars should never be used
as for the most obvious, they can easily break if accidently dropped and if
you have over catalyzed the resin or you have not used it all up or got
called away the jar could easily shatter causing small and large fragments
of hot glass and resin to fly in all directions for many meters which could
result in severe injury to ourselves and others as the resin begins to gel
or harden as there can be a lot of heat generated as resin sets.
Polyester based 2 packs can also deform these plastic type containers.

Spatulas :

You may need one of these to mix up gelcoat paste or filler (bog)
when your ready to finish off your fiberglass Spatulas
repair, these come in different sizes and shape,
but you usually get a plastic one when you buy a tin of filler anyway which work well.

Disposable plastic ones are good also because
you can trim or cut them to bog in corners.

Brushes :

If you do not have much fiberglass repair work to do and it is only
a small job and you have no intention of doing more, then a couple
of cheap disposable brushes should be all you need, that way it will
save you money not having to buy acetone to wash out your brush.

The size of the brush will to a degree depend on your job, for Brushes for fibreglass repair. fiberglass spoilers, cracks is fiberglass kit cars to canoes a 25mm (1") to 38mm (1½") will do the job.

If you were say using a hole saw to put in drains (bungs) in a new or existing transom (stern) of a boat (as a example) you would most likely use a 12mm (½") brush (as most drain bungs would be 25mm (1") to 35mm (1½") as the timber or foam core will need to be sealed with mat and resin to make sure of integrity of end grains is protected.

Sandpaper :

You will most likely be needing some sandpaper if your intentions are
to finish off your fiberglass repair to look like or blend in with the surrounding area, especially if your article is smooth, shiny and

The sandpapers you will be using will be dry paper and vary between
80, 150, 240 and 320 grit. Now, if you are doing to finish off with a
gel coat finish you will also need some wet and dry paper with a grit
of 800, 1200 and 2000 grit, but we will talk more of final coatings and what is best to finish off with under Fiberglass repair kits and materials, for now this is our tooling section.

Sanding block

Now these are good to have if your fiberglass repair article is flat to having a slight round in it. Sanding blocks

These can be bought as cork or a semi flexible to stiff rubber or you can make your own from a piece of ply/timber.
A piece of wooden dowel (broom handle) or small plastic pipe come in handy if your fiberglass repair has long corners in it as you can wrap your sandpaper around it to form a hard semi circle sanding block, good also for sanding inside or making holes bigger or cleaner.

Laminate rollers :

Laminate roller? what the hell is a laminate roller?.
For a start,the word "laminate" refers to a laminated structure or
material, especially one that is made of layers bonded together to form
a hard, flat, curved or flexible material like in this case fiberglass mat and resin. Laminate rollers.

The purpose of these rollers are to roll out any
air entrapments between layers of glass, fibers
and resin, helps to ensure an even and uniform resin saturation of fibers making for a strong, consistent, and solid laminate.

Giving a even, semi-finish to your fiberglass repair or laminate layup with no or little effort involved when applying fillers or flowcoats.

Laminating rollers come in various sizes and styles for different
applications.The most common laminating rollers are made from alloy and come in either a coin/ring grooved or paddle roller.

So, which one is better? The coin or ring roller is better suited to
chopper gun layups when more material is present, taking the air out
deeper in the laminate with due care taken as not to heap or push up
the laminate. A paddle roller is usually then used to finish off the
final layers to get rid of groove marks and even up for a flat surface.

The paddle roller will be your best choice here for mostly if not all
fiberglass repair work including replacements like hull bearers, stern replacements, floors or anything else you will likely to use fiberglass for.

Size will depend upon your fiberglass repair or layups involved, if your not sure of what size to buy, ask your fiberglass supplier but generally speaking a 80mm × 22mm (3¼"×.866") is a good roller for most work, for small or delicate work with small radius a bar roller 40mm×10- 12mm is good, for larger panels like floors or sterns a 120mm × 22mm (4¾ × .866") or a little bigger is good.

Different manufacturers will have slightly different sizes.
Next we will go into what fiberglass materials we need to buy to do
our repair.

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